A Long Island-born Kansas City Chiefs linebacker gunned down the mother of his 3-month-old daughter yesterday before driving to Arrowhead Stadium and killing himself in front of his head coach and his general manager, police said.

Jovan Belcher, 25, from West Babylon, thanked General Manager Scott Pioli and head coach Romeo Crennel for all their help before pacing 40 feet and putting a bullet in his head at around 8 a.m. in the stadium parking lot.

Belcher’s tragic ending came less than an hour after he fatally shot his girlfriend, Kasandra Perkins, who gave birth to their daughter, Zoey, on Sept. 11.

Belcher was furious with Perkins after she came home at about 1 a.m. from a Trey Songz concert, according to the Kansas City Star newspaper.

The two got into a heated argument in the home they share with Belcher’s mother, Cheryl Shepherd, who recently moved in with the couple to help with the baby, who was unhurt and being cared for by relatives.

At around 7:50 a.m. yesterday, Shepherd called 911 in a panic, saying a woman was just shot multiple times at the Crysler Avenue home five miles from the stadium.

“The young woman was taken to a local hospital, where she died a short time later,” said police spokesman Darin Snapp.

Neighbors recalled the early- morning gunplay — followed by Belcher’s black Bentley tearing out of the driveway.

“I was cooking breakfast when I heard a pop or a boom, and I thought it was something that fell over in my house,” said Kayetta Grant. “Then I saw a Bentley speed around the corner.”

“The description matched the suspect description from that other address,” Snapp said. “We kind of knew what we were dealing with.”

The player was “holding a gun to his head” as he stood in front of the front doors of the practice facility. Pioli and Crennel — at the stadium for the team’s practice — ran outside to talk down Belcher, cops said.

“No more violence, Jovan,” they said.

The coaches told cops they had never felt endangered, Snapp said.

“They said the player was actually thanking them for everything they’d done for him. They were just talking to him, and he was thanking them and everything.”

But they could do nothing to stop him.

“The suspect began to walk in the opposite direction of the coaches and the officers, and that’s when they heard the gunshot,” Snapp said.

Pioli — who is Bill Parcells’ son-in-law and a former Jets executive — was said to be “distraught.”

“He saw it all and sounded like he was in shock,” a friend told The Post.

Kansas City Mayor Sly James said he spoke with Pioli and that the GM was “very emotional.”

Chiefs Chairman and CEO Clark Hunt said in a statement, “The entire Chiefs family is deeply saddened by today’s events, and our collective hearts are heavy with sympathy, thoughts and prayers for the families and friends affected by this unthinkable tragedy.”

Belcher and Perkins had been introduced about three years ago by another Chiefs player.

Pictures on Perkins’ Facebook page show the two apparently in love, smiling in bed together with a dog licking Belcher’s face.

“Daddy is home from his game! We missed you!” Kasandra wrote under a photo, dated Oct. 9, 2011.

Perkins’ family told The Post she moved from Texas to Kansas City to be with her man, and everything seemed perfect.

“She had a boyfriend, and she was so happy, and she was having a baby,” said cousin Ebony Perkins.

“She was a great person. I don’t see what could have possibly been so bad. She was sweet and helpful and always looking to help other people.”

When Zoey arrived, the two showed off their bundle of joy in a series of photos marking happy occasions: a visit to the doctor, her first Halloween, and most recently on Thanksgiving.

Belcher’s family gathered yesterday in West Babylon to mourn his death.

“He was a beautiful person,” Belcher’s sister Charmaine Miles told The Post.

Another relative told The Post that he spoke to Belcher Friday and that all seemed normal.

“He was happy, he was fine, he was great. We were just cracking jokes and carrying on like we always do,” the person said.

“I don’t know what happened. He’s the last guy you’d think that could be capable of doing something like this. We don’t know how to feel.”

The 6-foot-2, 228-pound linebacker was in his fourth season with the Chiefs, his third as a full-time starter after joining the squad as an undrafted free agent.

He started 10 of the 11 games he played this season, making 38 tackles, and appeared in all 16 games each of his previous three seasons, amassing 257 tackles and one sack in his career.

In 2009, Belcher had the words “Reckless Abandon” tattooed on his body.

In a video posted on the Chiefs Web site Nov. 21, Belcher discussed things that made him thankful: “First and foremost, God. Family and friends just keeping me focused, coaches and just everyone.”

Belcher’s teammates took to Twitter to express their grief.

“I am devastated by this morning’s events. I want to send my thoughts and prayers out to everyone affected by this tragedy,” wrote Chiefs linebacker Tamba Hali.

The season has been a monumental disappointment for the Chiefs, who are stuck in an eight-game losing streak and whose 1-10 record ties them for the worst start in team history.

Belcher is the second Kansas City Chiefs employee to be involved in a murder-suicide in the past four months. Luis Angel Roberson Rodriquez — who worked in the team’s stadium operations department — committed suicide after shooting his girlfriend Jamie Kristine Kimble near the Tampa International Airport on Labor Day.

Kansas City is scheduled to host the Carolina Panthers today at 1 p.m. Eastern Time

Decade of off-field violence

Yesterday’s murder-suicide in Kansas City was but the latest in a long list of tragic gunplay involving NFL players. Here are some other examples:

2001: Carolina Panther wide receiver Rae Carruth, then 27, was convicted of conspiring to kill pregnant girlfriend Cherica Adams, 24. She was shot four times in her car in 1999.

2006: Cincinnati Bengal wide receiver Chris Henry was charged in Florida with concealment of a firearm and aggravated assault with a firearm. Three years later, he fell out of a truck being driven by his fiancée and died.

2007: Carolina Panther offensive tackle Jeremy Bridges was busted for allegedly pointing a gun at a woman in the parking lot of a Charlotte, NC, strip club.

2007: Chicago Bear tackle Tank Johnson was arrested on misdemeanor weapons charges after a police raid of his home uncovered six unregistered firearms and 550 rounds of ammunition.

2008: Giant wide receiver Plaxico Burress was charged with criminal possession of a weapon after he accidentally shot himself in a nightclub.

2011: Oakland Raider linebacker Rolando McClain was arrested on misdemeanor charges after allegedly holding a gun to a man’s head before firing it into the air.

2012: Cleveland Brown Kiante Tripp was arrested and charged with burglary and possession of a firearm.

2012: Former Oakland Raider defensive end Anthony Wayne Smith was charged with three Los Angeles murders — while awaiting retrial on an unconnected 2008 murder charge Smith pleaded not guilty.